Electro-hydraulic transducer

ABSTRACT

A liquid flowing through a restricted throttling passage is heated by the energy of an electric signal that it is desired to convert to a hydraulic signal, and the resulting increase in the temperature and the fluidity of the liquid causes increased flow through the passage, the increase constituting the hydraulic signal. Use of the hydraulic signal for controlling a slide valve is illustrated.

e w '"vvu Urllv Cyphelly Apr. 23, 1974 [54] ELECTRO-HYDRAULIC TRANSDUCER 1,911,066 5/1933 Doble 235/103 [76] Inventor: Ivan-Jaroshv yp y, 8128 3,678,243 7/1972 Ando et al. 1371341 Hinteregg, Switzerland F} d: M 3 Primary ExaminerAlan Cohan [22] l e ay Attorney, Agent, or Firm-Hans Berman [21] Appl. No.: 139,523

[30] Foreign Application Priority Data [57] ABSTRACT May 6, 1970 Switzerland 6822/70 1 Mar. 30, 1971 Switzerland 4593/71 A li id flowing through a restricted thrcttling passage is heated by the energy of an electric signal that it is [52] U.S. Cl. 137/828, 137/13 d i d to onvert to a hydraulic signaL-an'd the result- Cl. ing inc -ease in the temperature and of the [58] Field of Search 137/13, 341, 81.5; i i causes increased flow through the passage, the 236/103 increase'constituting the hydraulic signal. Use of the I hydraulic signal for controlling a slide valve is illus- [56] References Cited Hated 1 UNITED STATES PATENTS 3,334,641 8/1967 Bjornsen 137/13 6 Claims, 20 Drawing Figures mm mms m4 3.805843 sum u or 4 Fig. 77 X 11 Fig. 78 XVII electric signal that it is desired to convert. The resulting change in the flow rate of the liquid through the throttling zone constitutes a hydraulic signal which may be employed for controlling a valve or amplifier.

The known devices rely on moving parts and are subject to the limitations and shortcomings inherent in mechanical devices. It is an object of the invention to provide an electro-hydraulic transducer arrangement capable of operating without solid moving elements.

According to one of its more specific aspects, the invention provides a restricted throttling zone with electrically operated heating means which respond to the electric signal to be converted for varying the temperature, and thereby the viscosity or fluidity of a liquid supplied to the throttling zone under pressure. The liquid is guided through the zone in a predominantly laminar flow pattern. The change in viscosity produces a corresponding change in the flow rate of the liquid through the throttling zone, and the change in the flow rate provides the desired hydraulic signal.

According to another aspect, the invention resides in a method of converting an electric signal to a hydraulic signal inwhich a liquid is supplied under pressure to a restricted throttling zone. Theenergy of the electric signal is converted in the zone to thermal energy, and the latter is transmitted to the liquid in the zone, whereby the temperature and viscosity of the liquid are changed, and its flow rate through the throttling zone is increased, the increase in flow rate constituting the desired hydraulic signal.

Other features, additional objects, and many of the attendant advantages of this invention will readily become apparent as the invention becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the appended drawing in which:

FIG. 1 shows a first transducer arrangement of the invention in elevational section;

FIG. 2 illustrates the device of FIG. I'in section on the line II II; p g

FIG. 3 shows another transducer arrangement of the invention in elevational section;

FIGS. 4,5, and 6 respectively illustrate the device of FIG. 3 in section on the lines lV-IY, V-V, and VI- -VI;

FIGS. 7 and 8 illustrate a modified transducer in views corresponding to those of FIGS. 1 and 2 respec-, tively;

FIGS. 9 and 10 illustrate two additional transducer FIG. l4is a view of the device of FIG. 13 in fragmentary section on the line XIV-XIV;

. FIG. 15 is a sectional elevation of a valve operated by a transducer of the invention;

FIG. 16 shows a portion of the apparatus of FIG. 15 in an exploded perspective view on a larger scale;

FIG. 17 shows yet another transducer arrangement of the invention in fragmentary elevational section on the lineXVII-XVII in FIG. 18;

FIG. 18 illustrates the apparatus of FIG. 17 in section on the line XVIII-XVIII;

FIG. 19 is a diagram of a modification of the device of FIG. 17; and

FIG. 20 shows a modification of the devices of FIGS. 17 to 19 on a larger scale.

Referring now to the drawing in detail, and initially to FIGS. 1 and 2, there is seen a particularly simple transducer arrangement of the invention. A cylindrical metal tube 1 of limited electrical conductivity is secured at one end by a solder joint 2 in a relatively heavy mounting flange 3. The other end of the tube 1 is soldered to a lug 4 attached to a cable 5.

The tube 1 may consist of nickel-chromium or nickel-chromium-iron alloy of the type commonly employed in electric heating elements, but preferably consists of a titanium alloy containing at least 80% titanium or a zirconium alloy containing at least 50 percent zirconium, the titanium and zirconium alloys combining high electrical resistance with low heat capacity.

The steel flange 3 is normally fastened to a grounded metal object, and the liquid whose flow velocity is to be controlled is supplied to an orifice of the'tube 1- at a I longitudinally through the wall .of the tube 1 from the cable 5 to ground, the lug 4 being supported in the air by the tube 1, and thereby electrically insulated.

The current passing through the tube 1 heats the latter and the liquid in' the tube. The resulting temperature increase of the liquid, typically hydraulic fluid or oil, decreases the viscosity of the liquid, and the flow ratethrough the throttling zone provided by the tube 1 is increased. The hydraulic signal constituted by the increase in flow ratemay be used for controlling suitable devices as will presently become apparent.

FIGS. 3 to 6 showa modification of the transducer arrangement of FIGS. 1 and 2 in which the cross section of atube 1', otherwise closely similar to the tube 1, gradually varies from a circle at the tube end soldered to a flange 3' to a flattened loop at the end soldered to a lug 4'. For equal electric input and under otherwise equal conditions, the device of FIGS. 3 and 4 produces a greater change in the flow velocityor flow rate of a liquidthan that described above. The change arrangements of the invention in views corresponding to thatof FIG. 2;

FIG. 1 1 shows yet another transducer arrangement in elevational section;

FIG. 12 showsthe device of FIG. 11 in fragmentary section on the line XII-XII; i

FIG. 13 illustrates a further transducer arrangemen of the invention in elevational section;

is commensurate-to the ratio between the heating surface and the crosssectionalarea of the liquid.

The transducer arrangement illustrated in FIGS. 7 and 8 differs from that illustrated in FIGS. 1 and 2 by a tube 1". of uniform cross section similar to that shown in FIG. 6. Liquid flows through the tubefl'fas a relatively thin ribbon The flattened tube offers relatively little resistance .to internal liquid pressure and is therefore reinforced by circular discs 6 perpendicular to the tube axis and soldered to the tube 1'' in axially' spaced relationship. The discs 6 also constitute cooling ribs on the tube 1" which hasten return of the liquid temperature in the tube to ambient temperature as soon as the electric heating signal is interrupted.

A similar cooling effect can be achieved in the manner illustrated in FIG. 9 which shows only the tube 1 of the first-described embodiment spacedly enclosed in a jacket 7 through which a cooling fluid may be passed as indicated by curved arrows. The starting temperature of the liquid in the throttling tube may thus be selected at will and is independent of the ambient temperature.

While the liquid temperature in the devices of FIGS. 7 to 9 is quickly brought back to the starting temperature as soon as the electric signal is discontinued, and the flow rate of the liquid is correspondingly returned to its starting value, FIG. 10 shows an arrangement, identical with that of FIGS. 1 and 2, as far as not explicitly shown otherwise, in which the liquid flow rate responds with only a minimal delay to the application of an electric heating signal. v

The tube 1 is mounted coaxiallyin a glass tube 8, and the annular space between the tubes 1, 8 is evacuated! Thermal losses from the tube 1 are essentially limited in this arrangement to insignificant radiation losses,

and the flow rate through the throttling tube 1 quickly responds to an applied electric signal.-

In the devices described so far, the tube which guides the liquid through the throttling zone consists of electrically conductive material and alsofunctions as a heating elementrThis arrangement is structurally relatively simple, and heat transfer through the relatively large tube wall is effective. The response of the transducer-is inherently somewhat slow because the heating element also performs'structural functions and must be made heavy enough to withstand the internal hydraulic pressure, normally much higher than atmospheric 'pressure. Even with the use of materials'of constructions having low heat capacity, a lag in response is unavoidable. It is also difficult to produce sufficiently uniform tubing in the capillary dimensions (1 mm flow section or less) in which the throttling tubes of the invention are most useful. v

The response of the transducer arrangement to the electric input signal can be'hastenedby assigning the guiding and heating functions to separate structuralelements, that is, by installing a heating element coaxially in the conduit which guides the liquid flow in a predominantly-laminar pattern. Theithermal capacity of the heating element canbe reducedto'an insignificant value in such an arrangement. Nickel-chromium, nickelchromium iro'n, titanium alloys, zirconium alloys, and the like, may be employed for the heating elements as discussed above. '1.

In the transducer arrangement shown in: FIGS. 11' and l2, the throttling passage is partlyconstitutedby a bore 11in aheavy glass .plate:.l 2 which thermally insulates. the liquid flowin'g through thegbore 11. Metal washers 14a, l4baxially aligned wiht the bore 11 are fastened to the opposite surfacesrof theplate 12 and carry respective metal'bra'ckets 13a, 13b which have free ends axially'offset from the orifices of the throttling passage in the washers 1"4a,.14b. Aflat ribbon10 of. resistance wire is held under slight tension in the throttling passage between solder joints on the brackets Because of the relatively small heating surface of the ribbon 11, the application of the device shown in FIGS. 11 and 12 is limited, and only small changes in the temperature of hydraulic fluid or oil passing through the bore 11 can be achieved under many conditions.

Better heat transfer is obtained in the device shown in FIGS. 13 and 14, identical with that described in the preceding paragraphs except for a heating element 10' which is starshaped in cross section-and thus provides a more favorable heating surface-to-flow section area ratio than the ribbon 10.

FIGS. 15 and 16 illustrate the application of the aforedescribed transducer arrangements to the control of a hydraulic valve. In these Figures, an externally heated throttling conduit is being shown by way of Example as in FIGS. 1 to 10. It will be understood, however, that an internally heated throttling passage may be provided in the device shown in FIGS. 15 and 16 without significantly affecting the. operation of the apparatus.

. Referring initially to FIG. 15, there is seen a valve casing 26 which receivesa slidelvalve 15 in a stepped cylindrical bore-The valve'contr'olsflow of hydraulic fluid betwen a supply'conduit 25,. two operating conduits22, 23 and a return conduit-24.,A pump, not shown, withdraws returned fluid from a .sump 'connected to the conduit 24 and delivers it tothe conduit 25 at an'elevated pressure P; Inthe' illustrated neutral position of the valve 15, both operating conduits 22, 23 are blocked. When the valve moves toward the left, as viewed in FIG. 15, the operating conduit 22 is connected to the supply conduit 25, and the operating conduit 23 is vented to the non-illustratedsump-through the return conduit24. The flow in'the operating conduits 22, 23 is reversed when the valve moves toward the right from-theillustrated position. The valve arrangement described so :farisenti'rely conventional.

The narrow end of the stepped cylindrical bore in the valve casing 26 is permanently connected with theconduit 25, and the full pressureof the hydraulic fluid acts on the smaller end face 16 of the valve 15. In order to hold the valve l5 in the. illustrated positiomthe fluid pressure on a piston 17 of the valve 15 in the larger end of the stepped bore must assume a smaller value P P v mounted on the casing 26 and projectinglinto thelorifice ofan axial bore of the valve {15. The large end of 13a, 13b to which the electrical signal is applied by ca-g bles ina conventionalmanner, not shown.-

the tepped bore in the c'asin'giZG isconnected with the return conduit 24' by a'throttling tube 18 of theinven; tionandaninsulating'tubefl8f The flow rate through the tube l8may'be changedsby increasin'g or 'decrea s'r ing the output currentof a signal amplifier 21 to the in-- sulated end and to the grounded-end of the tube 18,.

The trimmer 19 iss et in such a manner that no fluid flows through the needle valve 20 as.long 'as,the'-. tube I8.is heatedzto aninterrnediate'value. When the tube 18 isheat'ed further, the pressure Pcan be maintained only by increasedflow of fluid through the needle valve 20, nd the valve 15 moves; from the illustrated position toward the right to providean adequate flow section at the needle valve '20. The oppositeeffect is" achievedibyl reducing the heating "current. i

The trimmer valve 19 is shown in more detail in FIG. 16. Its base plate 30 is normally bolted to the valve casing 26. A capillary tube 27 is sealed by soldering in two passages 28, 29 of the base plate 30 which communicate with the supply conduit 25 and the large end of the stepped valve bore in the installed throttle 19. The tube 27 is coiled in more than one turn about a threaded stud upwardly extending from the base plate 30. A washer 33 may be lowered on the tube 27 by means of a nut 32 engaging the stud 31 elastically to deform the tube 27 and thereby to reduce the effective flow section of the same.

When the transducer arrangements of the invention are provided with throttling tubes whose electrical resistance converts the electrical energy of an applied signal to thermal energy, it has been found advisable to protect the sensitive tubes against an electrical, and thus also a thermal overload.

A suitable protection arrangement is shown in FIGS. 17 and 18. The tube 41 expands mainly longitudinally when heated. It is fixedly attached by one longitudinal end to a grounded, conductive support 42 formed with a supply bore 42a and a discharge bore 42b of substantially greater flow section than the throttling tube 41 with which the communicate. The other longitudinal end is soldered to a lug 43 held in a fixed position on the support 42 by an interposed wafer 44 of insulating material. Heating current is supplied to the tube 41 by a cable 45 on the lug 43 and the ground connection of the support 42. Liquid flows through the tube between the bores of the support 42 and of the lug 43.

In the initially installed condition, the center of the tube 41 is laterally offset from a straight line through the two ends by a small amount. When heated by the passage of current, the tube 41 buckles as shown in broken lines at 41 to cut the beam 46 of a light source 47 which is directed toward a photo-electric cell 47. The cell is arranged in circuit with a relay, not shown, which interrupts the electric heating'signal fed to the tube 41 in a conventional manner evident from FIG. 19.

FIG. 19 diagrammatically illustrates a mechanical equivalent of the photoelectric safety switch arrangement described with reference to FIGS. 17 and 18. buckled, buckles, the tube 41 engages the actuating element 52 of a switch 53 and thereby interrupts the output circuit of an amplifier 51 which supplies heating current. The arrangement of FIG. 19 is somewhat less reliable'than that of FIGS. 17 and 18 because of the use of moving mechanical elements, and the aforedescribed safety arrangement is preferred.

The distance between the two fastened ends of the tube 41 must be maintained constant for a reproducible buckling effect. It is necessary, therefore, to prevent or at least to minimize heating ofthe supporting structure. This can be achieved in a simple manner as shown in FIG. 20. A terminal portiona of the tube 41 iscoated with a thin layer 54 of highly conductive metal, such as copper or silver, which provides a shunt across the terminal tube portion and prevents heating of the same and of the associated supporting structure by the passing electric current. The tube 41 is thin enough and made of material of sufiiciently poor thermal conductivity to prevent the flow of significant amounts of thermal energy through the terminal portion a. Heating of the support 42 by. the hydraulic fluid can be held to an insignificant value by making the support- 42 of alumiby attaching it to a heat sink, such as the valve casing 26 (FIG. 17).

It should be understood, of course, that the foregoing disclosure reated relates topreferred embodiments of the invention, and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. An electro-hydraulic transducer arrangement for converting an electric signal to a hydraulic signal, the arrangement comprising:

a. an elongated conduit having a longitudinal wall of electrically conductive material, said wall defining a longitudinal throttling bore in said conduit;

b. means for transmitting said electric signal to said wall, and for passing the transmitted signal longitudinally through said wall and for thereby heating said wall in response to said signal;

c. supply means for supplying a liquid under pressure to one longitudinal end of said bore for flow of said liquid through said bore; 1

t d. discharge means for discharging said liquid :fro

the other end of said bore,

1. said wall being shaped to guide said liquid through said bore in a predominantly laminar 2. the heating of said wall by said electric signal being sufficient to increase the'temperature of the flowing liquid and thereby decrease the viscosity thereof; and

e. safety means responsive to a predetermined longi- 3. In an arrangement as set forth in claim 2, said switch means including a light source and a photoelectric cell arranged in the beam of said light source, said conduit. interrupting said beam when buckled.

4. In an arrangement as set forth in' claim 2, a coating of ahighly conductive metal on said longitudinal ends of said conduit, the conduit consisting of metal having substantially greater resistivity than the metal of said coating. v

5. An arrangement as set forth in claim 1, wherein said supply means include a supply conduit communicating with said one end, and said discharge means include a discharge conduit communicating with said other end, the flow sections of said supply conduit and of said discharge conduit being substantially greater than the flow sectionof said throttling bore.

6. In an arrangement as set forth in claim 5, 'said throttling bore having an effective flow section riot sub stantially greater than lsquare millimeter. 

1. An electro-hydraulic transducer arrangement for converting an electric signal to a hydraulic signal, the arrangement comprising: a. an elongated conduit having a longitudinal wall of electrically conductive material, said wall defining a longitudinal throttling bore in said conduit; b. means for transmitting said electric signal to said wall, and for passing the transmitted signal longitudinally through said wall and for thereby heating said wall in response to said signal; c. supply means for supplying a liquid under pressure to one longitudinal end of said bore for flow of said liquid through said bore; d. discharge means for discharging said liquid from the other end of said bore,
 1. said wall being shaped to guide said liquid through said bore in a predominantly laminar flow pattern,
 2. the heating of said wall by said electric signal being sufficient to increase the temperature of the flowing liquid and thereby decrease the viscosity thereof; and e. safety means responsive to a predetermined longitudinal, thermal expansion of said wall for interrupting transmissIon of said electric signal to said wall.
 2. the heating of said wall by said electric signal being sufficient to increase the temperature of the flowing liquid and thereby decrease the viscosity thereof; and e. safety means responsive to a predetermined longitudinal, thermal expansion of said wall for interrupting transmissIon of said electric signal to said wall.
 2. In an arrangement as set forth in claim 1, said safety means including fastening means spaced along a straight line and holding the two longitudinal ends of said conduit at a substantially fixed distance while the remainder of said conduit is offset laterally from said line in one direction, whereby said conduit buckles laterally in said one direction when expanding thermally, and switch means responsive to a predetermined amount of buckling for interrupting said transmission.
 3. In an arrangement as set forth in claim 2, said switch means including a light source and a photoelectric cell arranged in the beam of said light source, said conduit interrupting said beam when buckled.
 4. In an arrangement as set forth in claim 2, a coating of a highly conductive metal on said longitudinal ends of said conduit, the conduit consisting of metal having substantially greater resistivity than the metal of said coating.
 5. An arrangement as set forth in claim 1, wherein said supply means include a supply conduit communicating with said one end, and said discharge means include a discharge conduit communicating with said other end, the flow sections of said supply conduit and of said discharge conduit being substantially greater than the flow section of said throttling bore.
 6. In an arrangement as set forth in claim 5, said throttling bore having an effective flow section not substantially greater than 1 square millimeter. 